1. Field of the Invention
This invention relates generally to the manufacture of semiconductor devices, and, more particularly, to a low temperature process for depositing an oxide dielectric layer on a conductive surface, and to multilayer structures formed by such a process.
2. Description of the Prior Art
In the fabrication of semiconductor devices and circuits it is often necessary to form a layer of an oxide dielectric on the surface of a metal or other conductive material, to provide electrical insulation which prevents contact or unwanted current flow between adjacent conductive materials. With the increased microminiaturization of semiconductor devices and circuits, such as in large scale integrated circuits, and the need for higher speed operation, adjacent functional elements within a circuit on a single plane are located closer together, and interconnections are stacked one on top of the other to form multilayer structures. An increased packing density of devices and circuits can be achieved in these multilayer structures since the substrate surface area consumed by interconnections is greatly reduced. However, this increased packing density produces a stringent demand for a high quality oxide dielectric between conductive layers.
One oxide dielectric material which is frequently used in semiconductor devices and circuits is silicon dioxide (SiO.sub.2), which has been formed in a variety of ways. The thermal oxidation of silicon is one of the oldest techniques for forming SiO.sub.2 on a silicon wafer and is accomplished by heating a silicon wafer to 900.degree. C. or higher in an oxygen-containing or water-containing environment, as discussed, for example by A. Amick, G. L. Schnable and J. L. Vossen in the publication entitled, "Deposition Techniques for Dielectric Films on Semiconductor Devices," in the Journal of Vacuum Science and Technology, Vol. 14, No. 5, Sept./Oct. 1977, pages 1053 to 1063. An oxide formed by this process is referred to herein as a "thermal oxide".
More recently, SiO.sub.2 layers have been deposited by thermally activated low pressure chemical vapor deposition (LPCVD) as described, for example, by Amick et al referenced above. In such a LPCVD process, the substrate is exposed to vapor phase reactants, such as silane and oxygen, which are heated to 450.degree. C. under reduced pressure to bring about a chemical reaction to form SiO.sub.2, which deposits on the substrate. An oxide formed by such a process is referred to herein as a "LPCVD oxide". Alternatively, a layer of SiO.sub.2 has been formed by a plasma-enhanced chemical vapor deposition process, as also described by Amick et al referenced above, in which the vapor phase reactants such as silane and oxygen, are subjected to a radio frequency discharge to create an ionized plasma of the reactant gases, which then interact to form the desired oxide, such as SiO.sub.2, as a reaction product.
Another method by which an oxide layer may be formed is a sputtering technique, which may be either reactive or non-reactive, as described by Amick et al referenced above. Using non-reactive sputtering, a disk of a selected oxide material, such as SiO.sub.2, is bombarded with inert ions to cause the oxide to vaporize and subsequently deposit on the substrate. Using reactive sputtering, a disk of silicon is bombarded with oxygen ions, which produces ionization of the silicon, and the vaporized silicon and oxygen ions then react to produce SiO.sub.2.
However, some difficulty has been encountered in each of the above-described processes in reproducibly forming a high quality oxide with low pinhole density, good step coverage, and good voltage breakdown characteristics, with acceptable process yield. In addition, in the particular case of the above-described low pressure chemical vapor deposition process for SiO.sub.2, the elevated temperature required for the deposition process (e.g. 45.degree. C.) causes the surface of certain conductive substrates, such as aluminum, to deform. Hillocks and spikes are produced on the conductive surface and protrude through the oxide dielectric deposited thereon, thus generating defects or pinholes which degrade the insulating properties of the oxide.
It is the alleviation of these prior art problems of forming a high quality oxide on a conductive surface and of the deformation of a conductive surface during the deposition of an oxide layer thereon to which the present invention is directed.